Method and geodetic device for surveying at least one target

ABSTRACT

The invention relates to a method for surveying at least one target using a geodetic device. According to said method, a camera of the device captures a visual image and surveys an angle and/or a distance to the target with geodetic precision, the angle and/or distance surveillance being supported or controlled by the visual image. At the same time of capture of the visual image at least two distance points of a distance image are captured as the spatial distribution of discrete distance points in the area of detection. When the visual image and the distance image are correlated with each other, the target is recognized or the measuring process is controlled.

The invention relates to a method for surveying at least one target, ageodetic device and a computer program product.

BACKGROUND

Since antiquity, a multiplicity of measuring apparatuses have been knownfor recording properties of defined points in a measuring environment,in particular of spatial data. The location of a measuring devicetogether with any reference points present, and direction, distance andangle to targets and measuring points, are recorded as standard spatialdata.

A generally known example of such measuring apparatuses is thetheodolite. An overview of geodetic measuring apparatuses of the priorart is provided by “Elektronische Entfernungs- und Richtungsmessung”[Electronic distance and direction measurement] by R. Joeckel and M.Stober, 4th edition, Verlag Konrad Wittwer, Stuttgart 1999 and“Electronic Distance Measurement” by J. M. Rüeger, 4th edition,Springer-Verlag, Berlin, Heidelberg 1996.

For controlling the measuring process, devices with camera/screencombinations which permit ergonomically advantageous use are alsoincreasingly being used in addition to systems having an eyepiece. Inaddition, target identification or target tracking and hencefacilitation and automation of the surveying process can be effected bythe recording of an optical image.

Thus, for example, EP 1 314 959 and WO 2004/036145 disclose geodeticmeasuring devices having an electronic display and control apparatus,which permit screen-based operation.

In the two-dimensional representation of the optical image, it ispossible to specify the points to which a measurement, i.e. thedetermination of distance and/or angle is made. On the basis of theimage, targets can be identified and tracked by image processingmethods, so that automated surveying is possible on this basis.

However, this image has no depth information at all, so that the imageprocessing methods are reliant on appropriate preliminary information,image-recording conditions, such as, for example, the pre-alignment of atarget plate, or image properties, such as, for example, brightness andcontrast. The possibilities for target identification and tracking arelimited by the purely visual capture. In particular, optical ambiguitiesas occur, for example, in the case of curved surfaces cannot beresolved. Thus, in a frontal recording under unfavourable lightconditions, a disc and a sphere appear as an identical image in bothcases.

The recording of purely visual images thus limits the control andautomation of measuring processes in terms of the environmentalconditions and target geometries.

For the production of topographies as static images with depthinformation, images of the Earth's surface or a celestial body arerecorded from at least two different angles in aerial photogrammetryduring a camera flight or a recording movement, from which images heightinformation, for example for the preparation of map material, can becalculated on the basis of the collinearity relationship. In modernimplementations of this method, photographs are digitized by scanningfor electronic further processing or are digitally recorded during theflight itself.

EP 1 418 401 discloses a method and an apparatus for aerial or spacephotogrammetry, in which distance measurements to sampling points areadditionally carried out using laser beams of a laser rangefinder duringa camera flight with an aircraft for recording images which can be usedin photogrammetry. The distance measurements are recorded in each casefor a set of image points and later used as constraints for thepreparation of a topography of the surface. Recorded distancemeasurements can moreover be used for optimizing the recording andflight parameters.

During the production of aerial images, preferably using a multilinesensor camera, distance measurements to sampling points which in eachcase are coordinated with a set of at least one image point areadditionally carried out here for the recording of image points. Thesedistance measurements are effected with laser rangefinders.

An alternative to conventional photogrammetry has arisen through thedirect distance measurement from the aircraft to individual points bymeans of laser-based distance measurement (LIDAR). However, this methodis not capable of providing further information to a comparable extent,for example in different spectral ranges. In addition, the imagerecording is effected by scanning, i.e. sequentially so that it is notsuitable in applications for which rapid availability of imageinformation is decisive.

Moreover, LIDAR systems having a scanning beam have disadvantages whichresult from the mechanical design. Either the entire device has to bemoved over the visual region to be recorded or the beam guidance must bedesigned to be variable in an otherwise invariable apparatus. Inaddition to the expense of such mechanically and/or optically demandingor complex solutions, they generally have only a low scanning speed andin addition have a comparatively high energy consumption.

Systems which are based on sequential capture of additional depth ordistance information moreover have problems of mechanical stability.Owing to the scanning movement and mechanical loads, for example due tovibration, the correlation of the distance measurements with the imagepoints of the visual image is not ensured or is ensured only atadditional expense.

SUMMARY

The object of the present invention is to provide a method and anapparatus for geodetic surveying, which permits improved targetrecognition.

A further object is to improve the control of the measuring process fora geodetic device of the generic type.

The invention is based on the concept of obtaining further depthinformation over the capture region of the visual image by additionaldistance measurements between recording system and surface, whichfurther depth information can be used for controlling the measuringprocess and for target recognition.

In a wider sense, the invention relates to all geodetic devices whichare optically aligned with measuring points by visual alignment means orsupport such alignment. In this context, the term “geodetic device” isgenerally intended always to mean a measuring instrument which hasapparatuses for measuring or checking spatial data. In particular, thisrelates to the measurement of distance and/or direction or angles to areference point or measuring point. In addition, however, furtherapparatuses, e.g. components for satellite-supported positiondetermination (for example GPS, GLONASS or GALILEO), may also bepresent, which can be used for supplementary measurements or datarecordings. In particular, such a geodetic measuring device is to beunderstood here as meaning theodolites and also so-called total stationsas tacheometers with electronic angle measurement and electroopticalrangefinder.

Equally, the invention is suitable for use in specialised apparatuseshaving a similar functionality, e.g. in military aiming circles or inthe monitoring of industrial structures or processes; these systems arehereby likewise covered by the term “geodetic device”.

According to the invention, a further component which is formed forrecording distance measurements to selected points or with definedorientations within the area of capture of the visual channel isintegrated into a geodetic device having a camera. The distancesrecorded by this component are correlated with points in the image ofthe visual channel so that information can be derived via the structuresvisible in the visual image.

For example, CCD or CMOS cameras are suitable apparatuses which capturean image having a multiplicity of image points and are available asrecording components of the visual image.

Various alternatives are available as means for recording distances.Firstly measurements can be carried out by a plurality of separaterangefinders simultaneously to all points or to a plurality of points inthe area of capture in groups in cohesion as a function of time, i.e.directly in succession, it being necessary to adjust the individualrangefinders with regard to the image points. Secondly, integratedsolutions, e.g. chips as two-dimensional arrangements of individualsensors with integrated distance-measuring functionality, are alsoavailable. Such Range Imaging Modules (RIM) have, for example, 32×32sensors in a matrix arrangement. By means of this matrix, a distanceimage can be recorded as a spatial distribution of discrete distancepoints in the area of capture. It is true that, with this number ofsensor points and hence distance image points, the lateral resolution isnot sufficient for performing precise control and identification taskson the basis of the distance image alone. By combination with the visualimage, however, the required depth information can be made available forthis. For example, the visual and the distance image can be superposedlogically or optically so that, for individual image points or groups ofimage points, their spacing or their average distance to the device isalso known.

Here, distance image is understood as meaning a two-dimensionalarrangement of measured distance values which cover at least a part ofthe area of capture of the camera with the cohesion necessary forcontrol or target recognition. Different levels of cohesion, forexample, for successive steps of target recognition with increasingaccuracy, can also be used. It may be sufficient if only a singledistance value is recorded for an image point or a group of imagepoints. In many cases, however, identifiable cohesive structures in thedistance image permit matching with structures of the visual image sothat objects in the area of capture can be identified and can beclassified with respect to the distance or the sequence in the area ofcapture.

The implementation of the method on the apparatus side can be effectedboth with the use of separate components for distance measurement andimage recording and with integration of both functions into individualcomponents. The distance measurement carried out with the distancemeasuring points from a predetermined reference point in the device to adistance point in the area of capture must be capable of being relatedto the visual image recording so that various orientations andarrangements of the different components are possible as long as thiscondition is fulfilled. The reference point defining the distancemeasurement is generally determined by the design and the arrangement ofthe component recording the distance image in the device.

The distance points recorded by the means for recording a distance imageor the orientation of the axes of the distance measurements can bedistributed randomly or with a specific pattern within the area ofcapture of the visual image. Since in general only parts of the area ofcapture have to be more greatly resolved for target recognition and/orsurvey control, the position and density of the distance points may alsobe variable. Consequently, stepped methods are also possible, in whichfirst a visual or distance image-based coarse search run or coarsesighting is effected, followed by the higher resolution in a smallerarea. For this purpose, beam-modifying components, for example, arraysof microlenses or holograms, can be introduced, for example, into thebeam path before the means for recording a distance image. Alternativelyor in addition, however, the means itself can be moved within the beampath. Examples for realising a movement of components relative to thebeam path inside the device or for varying the emission and receptiondirection in an otherwise unchanged area of capture of the opticalsystem are described in WO 2004/036145.

The choice of the arrangement of distance points to be recorded can alsobe controlled on the basis of distance information. Thus, for example,in a first step, a distance image of the total area of capture can berecorded. In this distance image, regions with particularly greatvariance of the recorded distances are subsequently identified and arerecorded with high resolution and analyzed in a second step.

BRIEF DESCRIPTION OF THE DRAWINGS

The method according to the invention and a device according to theinvention are described or explained in more detail purely by way ofexample below with reference to working examples shown schematically inthe drawing. Specifically,

FIG. 1 shows the diagram of the components of a geodetic deviceaccording to the invention;

FIG. 2 shows the diagram of a first distribution of distance points tobe captured in the area of capture;

FIG. 3 a-d show the diagram of further distributions of distance pointsto be captured in the area of capture;

FIG. 4 shows a use example for a method or geodetic device according tothe invention;

FIG. 5 shows the diagram of visual image and distance image;

FIG. 6 shows the assignment of visual image and distance measurements tothe recording of a distance image and

FIG. 7 shows the diagram of an example for a distance image.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the diagram of the components of a geodetic deviceaccording to the invention. The total system consists of the assembliesfore-optics 1, autofocus and zoom group 2, infinite platform 3 andfinite platform 4 and optionally an eyepiece unit 6. The infiniteplatform 3 carries the components transmitter 9 and receiver 10 for adistance measurement to target object, illuminating laser 8 and receiverunit 11, for automatic target recognition. The beam paths ofilluminating laser 8, transmitter 9 and receiver 10 can be variedtogether by a microscanner element 12 so that surveying of the target orautomatic target recognition is possible in the area of capture. Targetrecognition is based here on the increased reflectivity of a cooperativetarget compared with the background. An improvement, according to theinvention, of the control and of the target recognition is permitted bythe integration of an RIM sensor array 7 into the finite platform 4.This RIM sensor array 7 makes use of a common beam path with a camera 6.Both components use the autofocus and zoom group 2, after which they areintegrated into the beam path. In this working example, camera 6 and RIMsensor array 7 are fixed in position relative to one another so that thedistance points to be recorded or the orientations of the distancemeasurements to points in the area of capture are coordinated in eachcase with individual image points or image point sets of the camera 6.

In alternative working examples, the assignments to the image points orthe geometry of the arrangement of the sensor points of the RIM sensorarrays 7 can be varied. For this purpose, either the RIM sensor array 7can be moved in the beam path and/or the beam guidance can be changed,for example by the introduction of microlens arrays or holographicelements into the beam path. This introduction is possible, for example,by rotatable support discs or displaceable linear arrangements, whichare not shown here.

FIG. 2 shows the diagram of a first distribution of distance points 16to be captured in the area 14 a of capture. By means of a total stationas geodetic device 13, a ground section to be surveyed is recorded inthe area 14 a of capture. Within the area 14 a of capture, angle anddistance measurements are made to selected measuring points 15 for thesurveying of which the geodetic device 13 is actually used. Parallel tothe recording of the area 14 a of capture by a camera, the distancemeasurement is made to distance points 16 which, in this example, have afirst distribution in a regular pattern, the pattern substantiallycovering the entire area 14 a of capture. Such a first distribution canbe realised, for example, by a plurality of separate distance-measuringunits or by a sensor array with a preliminary optical element for beamguidance or for divergence or alignment of beam axes with the sensorpoints. A comparatively large area 14 a of capture can be coveredthereby even with only a few sensor points or distance-measuring units.The distance measurement to the distance points 16 is effectedsimultaneously for at least two distance points 16, but preferably forthe entire distribution of the distance points 16 at the same time andin one process. If appropriate, however, a plurality of groups of ineach case at least two distance points 16 can also be sequentiallyrecorded, for example if a sensor array having only a few sensors is tobe used in order nevertheless to survey a relatively large number ofdistance points 16. By simultaneous distance measurement to at least twodistance points 16, but in particular a plurality of distance points 16or many distance points 16, it is possible to combine the visual imagewith distance information in real time. Simultaneity of the measurementmeans at least the overlapping of the distance measurements to the atleast two distance points 16 with respect to time.

If the distance information is provided at a rate which corresponds tothe optical recording rate of the visual image or to the userinteraction with the use of the visual image, there is no undesiredretardation of this visually controlled process. This is the case inparticular if distance measurement to the distance points 16 and captureof the visual image are effected simultaneously, the simultaneity—inaddition to a physical simultaneity—being determined by the rate ofcapture of the visual image or the user actions which thus determine theresolution required with respect to time.

A simultaneity prevents any possible deviations and differences betweenthe orientation in the distance measurement to the distance points 16and the capture of the visual image. These two processes can thereforeadvantageously be carried out simultaneously and in particular with theuse of an at least partly common beam path or jointly used components.This synchronous or simultaneous recording of distance measurements andvisual image ensures linkability of the two methods of measurement owingto the cohesion with respect to time, so that, for control of theapplication processes, distance information can additionally be used foridentification of structures in the visual image. The simultaneitypermits delay-free implementation of the process controlled via thevisual image, which will not be realizable in this manner, for example,in recording of distance measurements with scanning of points.

FIG. 3 a-d show examples of further distributions of the distance pointsto be captured in the area of capture. In these FIG. 3 a-d, as also inFIG. 2, only a few distance points to be captured are shown purely byway of example. The number of points to be used or of coordinated sensorpoints or distance-measuring units can, however, be substantiallylarger, e.g. 32²=1024, or even smaller.

FIG. 3 a shows a statistical or random distribution of the distancepoints in the area of capture.

FIG. 3 b shows the case of a regular pattern with equidistant rows andcolumns, as realised, for example, in RIM sensor arrays. This patternfor the most part fills the area of capture uniformly.

Another, hexagonal arrangement of the distance points is shown in FIG. 3c. This pattern approximates a circular area better than rectangularshapes. Here, a concentration of the distance points in the generallymost intensively used centre of the area of capture is shown. If thedimensions of the hexagon are chosen to be larger the pattern fills thearea of capture more uniformly than in FIG. 3 d.

Finally, FIG. 3 d shows a pattern which can be moved in the area ofcapture and can be positioned in zones of greater relevance. In thisexample, the buildings are the target of a survey, whereas the sky orthe groups of trees have no relevance for the survey. To increase theresolution, all distance points can now be moved in a part of the areaof capture, for example by changing the orientation of the beam axes.

FIG. 4 explains the method according to the invention or a geodeticdevice 13 according to the invention on the basis of a use example forautomated target recognition. By means of a total station as geodeticdevice 13, a plumb staff 17 having a reflector as a cooperative targetis to be detected and automatically sighted in built-up terrain. Awindow of a building 18 present in the area 14 b of capture may resultin reflections which may complicate identification of the plumb staff 17simply on the basis of its high albedo. Similarly disadvantageousconfigurations may also arise, for example, if the sun is low in the skyor in the case of road traffic with reflective vehicle surfaces.Particularly for non-cooperative targets, automated target recognitioncannot be performed under such conditions.

For automated detection of the plumb staff 17, the latter is, as shownin FIG. 5, recorded by the camera of the total station in a visual imageVB. This visual image VB likewise contains parts of the building 18 withreflective surfaces. The recording of a distance image, the recordingsensor array of which is composed of a matrix of sensor points for themeasurement of the distance points DP, is effected in parallel with thiscapture. In this example, the coverage achieved by the matrix of thedistance points DP corresponds to the visual image VB and hence to thearea of capture of the device, in each case a plurality of image pointsof the visual image VB being coordinated with each distance point DP.

By means of the sensor points, the distance points DP are surveyed withthe resolution shown in FIG. 6. In FIG. 6, the positions of the plumbstaff 17 and of the building 18 are emphasised within the distancepoints DP in the upper picture. The distances measured for theindividual distance points are shown in the lower picture for a row ofdistance points DP. In this purely exemplary representation thedifference between measured distance d and an assumed maximum distance Dis plotted. For non-determinable distance values, e.g. in measurementstowards the sky, for example, a predetermined value can be taken as aplace-holder value. For each of the pixels N_(ij), the associated valuefor D-d is given, resulting in a distance profile in which the plumbstaff 17 and the building 18 can be identified as structures in the areaof capture.

FIG. 7 shows the diagram of the distance image recorded according toFIG. 6, as an example for the identification of structures and theassignment of image points. The matrix of the distance points with therespective distance values D-d is shown. In this matrix, it is possibleto identify cohesive regions of distance values which can be coordinatedwith the structures of the visual image. Thus, in the distance image, afirst region can be identified as an image 17 a of the plumb staff, anda second region 18 a as an image of the building. The identification andassignment of the regions to objects in the visual image can beeffected, for example, by known image processing methods. In principle,structures can be identified here separately in each case for visualimage and distance image, which structures are combined in a subsequentstep or direct assignments of image and distance points can bemade—without separate structure recognition in the two images—from theaggregate of which the objects or structures are identified.

The embodiments and figures shown represent only explanatory examplesfor realisations according to the invention and are therefore not to beunderstood as being definitive and limiting. In particular, the numbersof the image points and distance points shown have been chosen merelyfor reasons of representation.

1. A method for surveying at least one target by a geodetic device,comprising: capturing a visual image of an area by a camera of thedevice, the camera obtaining a multiplicity of image points; performinga geodetic angle and/or distance measurement to the target, the angleand/or distance measurement being supported or controlled by means ofthe visual image; and simultaneously recording distance values of amultitude of discrete distance points for the provision of a distanceimage as a spatial distribution of discrete distance points in the areaof capture, wherein the number of distance points is smaller than thenumber of image points, wherein: the at least one image point iscoordinated with at least one distance point; and an orientation of thedistance measurements in the area of capture is varied, as a function ofmeasured distance values, in particular as a function of thedistribution of the distance values.
 2. A method according to claim 1,wherein the orientation of the distance measurements in the area ofcapture takes place according to a stochastic pattern.
 3. A methodaccording to claim 1, wherein the orientation of the distancemeasurements in the area of capture takes place according to a regularpattern.
 4. A method according to claim 1, wherein cohesive regions ofdistance points are identified in the distance image.
 5. A methodaccording to claim 1, wherein the visual image and the distance imageare superposed.
 6. A method according to claim 4, wherein, in the visualimage objects are identified on the basis of a correlation of cohesiveregions and features of the visual image.
 7. A method according to claim1, wherein the spatial position of an object, in particular of thetarget, in the area of capture is derived from the distance image.
 8. Amethod according to claim 1, wherein the spatial sequence of a pluralityof objects in the area of capture is derived from the distance image. 9.A method according to claim 1, wherein an identification of an object,in particular target recognition, is affected on the basis of thedistance image.
 10. A geodetic device for carrying out the methodaccording to claim 1, comprising at least: a camera for capturing avisual image of an area of capture, the camera obtaining a multiplicityof image points; an angle- and/or distance-measuring component; acontrol unit for controlling the angle and/or distance-measuringcomponent; and means for simultaneous recording of distance values of amultitude of discrete distance points and providing a distance image asspatial distribution of discrete distance points in the area of capture,wherein the number of distance points is smaller than the number ofimage points.
 11. A geodetic device according to claim 10, wherein thenumber of distance points recorded by the means for recording a distanceimage is smaller than the number of image points, at least one imagepoint being coordinated with at least one distance point.
 12. A geodeticdevice according to claim 10, further comprising a focusing member in abeam path to the camera, the means for recording a distance image beinga range imaging module sensors array and/or being arranged after thefocusing member in the beam path.
 13. A geodetic device according toclaim 12, further comprising means which can be introduced into the beampath, in particular in conjunction with a rotatable or displaceablesupport element, for orientation of the distance measurements in thearea of capture, in particular having microlenses or holographicelements.
 14. A non-transitory computer program product having programcode which is stored on a machine-readable medium for carrying out themethod according to claim
 1. 15. A method according to claim 5, wherein,in the visual image objects are identified on the basis of a correlationof cohesive regions and features of the visual image.
 16. A geodeticdevice according to claim 11, further comprising a focusing member in abeam path to the camera, the means for recording a distance image beingarranged after the focusing member in the beam path.
 17. A methodaccording to claim 1, wherein the simultaneous recording of the at leasttwo discrete points for the provision of a distance image as a spatialdistribution of the discrete distance points in the area of capture isperformed simultaneously with the capture of the visual image.
 18. Amethod for surveying at least one target by a geodetic device,comprising: capturing a visual image of an area by a camera of thedevice, the camera obtaining a multiplicity of image points; performinga geodetic angle and/or distance measurement to the target, the angleand/or distance measurement being supported or controlled by means ofthe visual image; and simultaneously recording distance values of amultitude of discrete distance points for the provision of a distanceimage as a spatial distribution of discrete distance points in the areaof capture, wherein: the number of distance points is smaller than thenumber of image points; and an orientation of the distance measurementsin the area of capture is varied as a function of measured distancevalues as a function of the distribution of the distance values.
 19. Ageodetic device according to claim 10, wherein the geodetic device is atacheometer, the camera is a CCD or CMOS camera and the control unitcontrols the angle and/or distance-measuring component by means of thevisual image.